The invention relates to optical signal processors and particularly to a hybrid digital/optical two-dimensional spectrum analyzer system using one-dimensional optical components and a digital memory.
Spectrum analysis is a fundamental technique utilized in a wide range of scientific fields. The usefulness of optical spectrum analysis in particular, has increased in the past few years due to its fundamental simplicity and inherent speed of operation, the ready availability of various critical optical components, and the extensive variety and versatility of the optical system architectures that have developed from basic optical systems.
An important feature of the optical spectrum analysis system is its inherent capability of performing wideband spectrum analysis on a real-time basis with many simultaneous signals present; for example, the entire broadcast band. In general, optical spectrum analysis provides relatively wider processing bandwidths than previously possible, at relatively higher data rates, utilizing optical components which are generally available as off-the-shelf hardware.
Optical spectrum analyzers generally are divided into two categories and thus architectures; a space integrating architecture which performs a Fourier transform with respect to a spatial variable, and a time integrating architecture which performs the transform with respect to a temporal variable. In addition, there are one and two dimensional transforms respectively, for both categories of analyzer systems.
As well known in the art, one-dimensional optical components have various inherent advantages over comparable two-dimensional components. One-dimensional signal processing provides increased bandwidth as when utilizing, for example, acousto-optical (A/O) cells such as Bragg cells, as the input transducer. Such cells also exhibit a greater dynamic range than currently is available in two-dimensional optical transducers. Likewise, one-dimensional charge coupled device (CCD) linear diode arrays utilized as adjunct components in, for example, a spectrum analyzer system, are less complex and exhibit a greater dynamic range as well as higher data rates than comparable two-dimensional arrays. For example, there are linear devices on the market that exhibit data rates of the order of 100 megahertz (MHz). Other linear devices presently are being offered which have a lower data rate but a dynamic range resulting in contrast ratios of 10,000 to 1. The main disadvantage of one-dimensional component systems is the limited time-bandwidth product resulting in lower processing gain, and, lower system resolution. Time-bandwidth product is the processing time (Tp) of, for example, an A/O cell multiplied by the processing bandwidth.
The main advantage of two-dimensional optical components for two-dimensional signal processing is the resulting high time-bandwidth product that is achieved. Such two-dimensional signal processing is performed utilizing devices such as, for example, a liquid crystal light valve in real-time systems, or recording film in non-realtime systems. Light valves such as those manufactured by General Electric, also are used in two-dimensional processing systems. None of the above devices are truly satisfactory in providing optimum two-dimensional signal processing for various reasons such as, for example, undue complexity, relatively slow processing rate and thus data rate, limited resolution, and/or lack of availability of specific optical components.
The present invention overcomes the disadvantages inherent in two-dimensional optical signal processors, while providing a spectrum analyzer system with all the advantages of one-dimensional optical components. A hybrid digital/optical system architecture combines high quality one-dimensional input transducers, such as A/O cells, with one-dimensional output transducers such as CCD arrays, to provide the functions and results of a two-dimensional spectrum analyzer.
To this end, one-dimensional optical architecture is combined with a digital memory system which, when properly controlled and formatted, supplies a signal to a second one-dimensional optical architecture, to ultimately achieve two-dimensional signal processing in real time. Such a combination is made possible by further providing means for preserving the phase relationship in the frequency domain of the signal supplied to the one-dimensional optical architecture.
To illustrate, an input signal to be processed is summed with a linear, frequency-modulated (FM) phase reference signal that is used to preserve the input signal phase relationship in the frequency domain. The combined signal and reference waveform are processed through an analog signal formatter, and form the input to a generally typical one-dimensional optical spectrum analyzer subsystem (OSA). A time history of the signal is stored in a digital corner-turn memory system in a time/frequency domain. The output of the memory system then is read with an address map that corner-turns the time/frequency axis. The resulting corner-turned output in the frequency/time domain is processed through a second one-dimensional optical spectrum analyzer subsystem (OSA) which supplies two-dimensional analog information in a frequency/frequency plane. The information contained in the plane may be selectively displayed via a suitable display system, or may be digitized and used to fill a second memory or to interface directly to a system computer, etc.
In addition, multiple hybrid digital/optical spectrum analyzer (DOSA) systems may be selectively combined to provide any of various additional system output signals.
Accordingly, it is an object of the invention to provide two-dimensional optical spectrum analysis utilizing one-dimensional optical components.
It is another object to provide hybrid digital/optical signal processing utilizing one-dimensional optical architecture with digital memory storage to achieve two-dimensional signal processing.
It is still another object to provide two-dimensional signal processing with one-dimensional optical architecture by preserving the phase relationship of the processed signal in the frequency domain.
A further object is to provide multiple signal processing with several processing functions simultaneously, via selected one-dimensional acousto-optical input transducers and time multiplexed input channels
Yet another object is to provide multiple digital/optical spectrum analyzer systems configured to supply cross correlation outputs, ambiguity surface information, etc.